大概念

        这个参数类型是PHPickerFilter，可选值混合了大概念和小概念，大概念：

• images 所有图片类型，包括LivePhoto（图片+0.5秒的视频）
• videos 所有视频类型

小概念

        除了两个大概念之外都是小概念

组合操作

        有三个诡异的方法，其实是用来组合的，因为苹果很贴心地屏蔽了内部实现嘛（位运算嘛，一般人容易出错）：

• all = AND，参数里面的都做AND啊，基本上就啥也不剩了
• any = OR，这才是组合各种类型的方法
• not = NOT，排除某种类型，可以用于在大概念里排除小概念

另：

        返回的选中项是PhotosPickerItem，可用的方法不多，除了loadTransferable(type: Data.self)别的都不可用，无法使用loadTransferable返回URL或UIImage（可以通过Data获得），itemIdentifier也是空的，supportedContentTypes倒是能用，只是内容是一大串文本。

参考：

static let bursts: PHPickerFilter
        A filter that represents assets with multiple high-speed photos.
static let cinematicVideos: PHPickerFilter
        A filter that represents videos with a shallow depth of field and focus transitions.
static let depthEffectPhotos: PHPickerFilter
        A filter that represents photos with depth information.
static let images: PHPickerFilter
        The filter for images.
static let livePhotos: PHPickerFilter
        The filter for live photos.
static let panoramas: PHPickerFilter
        A filter that represents panorama photos.
static let screenRecordings: PHPickerFilter
        A filter that represents screen recordings.
static let screenshots: PHPickerFilter
        A filter that represents screenshots.
static let slomoVideos: PHPickerFilter
        A filter that represents slow-motion videos.
static let timelapseVideos: PHPickerFilter
        A filter that represents time-lapse videos.
static let videos: PHPickerFilter
        The filter for videos.
static func any(of: [PHPickerFilter]) -> PHPickerFilter
        Returns a new filter formed by OR-ing the filters in a given array.